The performance of hydraulic systems is increasing, and the systems themselves are getting smaller. Reduced gap tolerances in valves, pumps and engines and better surface qualities allow higher operating pressures and enable system components to work more precisely. At the same time, ever increasing system availability, even under extreme operating conditions, is required. However, smaller oil charges, higher pressures and increased operating temperatures create intensified working conditions which a conventional mineral-oil-based hydraulic oil in class HLP or HLPD can barely withstand. All lubricants and power transmission media also age during their lifetime. This ageing process is caused in part by oxidation. High temperatures, long service lives, high pressures and in some cases even contaminants and wear particles all accelerate the ageing process. In order to delay ageing for as long as possible, the fluids contain antioxidants. However, these can also decompose during oil use, just like extreme pressure agents or anti-wear agents. With the addition of extreme operating conditions, temperatures increase as a result of power dissipation, which further accelerates oil ageing. And throughout this process, the viscosity of the oil also decreases, which is a key factor affecting the efficiency of the hydraulic system. Extensive tests with vane pumps, gear pumps and piston pumps have demonstrated that the viscosity of the hydraulic fluid has a considerable effect on the efficiency of the pump. Its hydraulic efficiency is dependent on the oil viscosity at the pump inlet, as well as on the pump speed and pressure. Therefore, the oil viscosity not only affects the efficiency of the pump as a whole but the energy consumption as well. For this reason, the viscosity of the hydraulic fluid should remain as constant as possible for the entire period of operation, from start-up right up to high-load operation. To ensure this, increasingly hydraulic oils with multi-grade characteristics of type HVLP or HVLPD are being used, which, in contrast to HLP oils, have a very high viscosity index of almost 200. In principle, these types of oils have a positive effect on energy consumption because even at temperatures of over 80 °C the minimum viscosity is not exceeded. However, the relatively high proportion of viscosity index improvers often present in the multi-grade oils can impair the air separation ability to such an extent that cavitation damage starts to appear. To avoid this as much as possible, hydraulics manufacturers allow oils that are thinner, with the result that the maximum permissible temperature for use of these types of oils must be reduced. This is the only way to be on the safe side in case of any shearing of the viscosity index improvers. In practice, the use of these multi-grade hydraulic oils at low start-up temperatures is ideal, but at very high operating temperatures they reach their limits. If the fluid becomes too „thin“, the hydraulics in construction machinery, for example, become more difficult to control or start to work imprecisely. In an attempt to resolve this dilemma, one of the leading international additive manufacturers has designed a special package of hydraulic oil active agents that is used by a number of lubricant manufacturers. The ready-made products, which are usually based on base oils in Groups I or II, meet the requirements of DIN 51524/3 for HVLP hydraulic oils. The new technology allows low-viscosity hydraulic oils to be used over a wider operating temperature range. This means that the efficiency of the hydraulic systems is increasing, while the energy consumption of the systems is decreasing. Compared to a conventional HLP hydraulic oil, the efficiency of the machine overall can only be increased by changing the type of oil. In practice, this means higher hydraulic pressures under full load, more precise reaction of the system and, above all, reduced energy consumption, meaning a reduction in the resultant oil temperature and energy-intensive cooling output. The manufacturer of the additive package expects a potential efficiency increase of around 5% and has demonstrated this in mobile hydraulic systems with extensive field tests. Whether using one of the somewhat expensive fluids included in the innovative additive package pays off simply on account of the reduced energy consumption must be considered on a case-by-case basis.